Interesting project. I'm curious to see how well it works in practice. Are you planning to have one of the PIDs off to maintain temps and use both in manual mode to ramp temps?
I assume you are thinking about large temp changes here, like protein rests and the like. But my experience in ramping mashes following protein rests is not good. A lot of protein gunk and a definite danger of scorching in my experience. I don't think I'd do it again without stopping to clean out the RIMS tube and element before ramping. I've personally moved to using a 220V element at 120V to maintain mash temps and minimize scorching issues.
While I ramp 10 or 20 degrees for mashouts, I think there's a danger there. Additionally, I used to have a RIMS tube like yours, but moved to a tri-clamp once I saw how crusted up the elements can get, even with circulation and even soaking in oxy.
Though it's not as elegant, I think infusing boiling water from HLT may be the best way. But that's just my limited experience. A lot people never have scorching issues at all.
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